This is a list of papers on atmospheric carbon monoxide with an emphasis on the observations and on the relation to fossil fuel sources. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.
UPDATE (May 16, 2012): Wang et al. (2012) added.
The isotopic record of Northern Hemisphere atmospheric carbon monoxide since 1950: implications for the CO budget – Wang et al. (2012) “We present a 60-year record of the stable isotopes of atmospheric carbon monoxide (CO) from firn air samples collected under the framework of the North Greenland Eemian Ice Drilling (NEEM) project. CO concentration, δ13C, and δ18O of CO were measured by gas chromatography/isotope ratio mass spectrometry (gc-IRMS) from trapped gases in the firn. We applied LGGE-GIPSA firn air models (Witrant et al., 2011) to correlate gas age with firn air depth and then reconstructed the trend of atmospheric CO and its stable isotopic composition at high northern latitudes since 1950. The most probable firn air model scenarios show that δ13C decreased slightly from −25.8‰ in 1950 to −26.4‰ in 2000, then decreased more significantly to −27.2‰ in 2008. δ18O decreased more regularly from 9.8‰ in 1950 to 7.1‰ in 2008. Those same scenarios show CO concentration increased gradually from 1950 and peaked in the late 1970s, followed by a gradual decrease to present day values (Petrenko et al., 2012). Results from an isotope mass balance model indicate that a slight increase, followed by a large reduction, in CO derived from fossil fuel combustion has occurred since 1950. The reduction of CO emission from fossil fuel combustion after the mid-1970s is the most plausible mechanism for the drop of CO concentration during this time. Fossil fuel CO emissions decreased as a result of the implementation of catalytic converters and the relative growth of diesel engines, in spite of the global vehicle fleet size having grown several fold over the same time period.” Wang, Z., Chappellaz, J., Martinerie, P., Park, K., Petrenko, V., Witrant, E., Emmons, L. K., Blunier, T., Brenninkmeijer, C. A. M., and Mak, J. E.: The isotopic record of Northern Hemisphere atmospheric carbon monoxide since 1950: implications for the CO budget, Atmos. Chem. Phys., 12, 4365-4377, doi:10.5194/acp-12-4365-2012, 2012. [full text]
Global estimates of CO sources with high resolution by adjoint inversion of multiple satellite datasets (MOPITT, AIRS, SCIAMACHY, TES) – Kopacz et al. (2010) “We combine CO column measurements from the MOPITT, AIRS, SCIAMACHY, and TES satellite instruments in a full-year (May 2004–April 2005) global inversion of CO sources at 4°×5° spatial resolution and monthly temporal resolution. The inversion uses the GEOS-Chem chemical transport model (CTM) and its adjoint applied to MOPITT, AIRS, and SCIAMACHY. Observations from TES, surface sites (NOAA/GMD), and aircraft (MOZAIC) are used for evaluation of the a posteriori solution. Using GEOS-Chem as a common intercomparison platform shows global consistency between the different satellite datasets and with the in situ data. Differences can be largely explained by different averaging kernels and a priori information. The global CO emission from combustion as constrained in the inversion is 1350 Tg a−1. This is much higher than current bottom-up emission inventories. A large fraction of the correction results from a seasonal underestimate of CO sources at northern mid-latitudes in winter and suggests a larger-than-expected CO source from vehicle cold starts and residential heating. Implementing this seasonal variation of emissions solves the long-standing problem of models underestimating CO in the northern extratropics in winter-spring. A posteriori emissions also indicate a general underestimation of biomass burning in the GFED2 inventory. However, the tropical biomass burning constraints are not quantitatively consistent across the different datasets.” Kopacz, M., Jacob, D. J., Fisher, J. A., Logan, J. A., Zhang, L., Megretskaia, I. A., Yantosca, R. M., Singh, K., Henze, D. K., Burrows, J. P., Buchwitz, M., Khlystova, I., McMillan, W. W., Gille, J. C., Edwards, D. P., Eldering, A., Thouret, V., and Nedelec, P., Atmos. Chem. Phys., 10, 855-876, doi:10.5194/acp-10-855-2010, 2010. [full text]
Comparison of adjoint and analytical Bayesian inversion methods for constraining Asian sources of carbon monoxide using satellite (MOPITT) measurements of CO columns – Kopacz et al. (2009) “We apply the adjoint of an atmospheric chemical transport model (GEOS-Chem CTM) to constrain Asian sources of carbon monoxide (CO) with 2° × 2.5° spatial resolution using Measurement of Pollution in the Troposphere (MOPITT) satellite observations of CO columns in February–April 2001. Results are compared to the more common analytical method for solving the same Bayesian inverse problem and applied to the same data set. The analytical method is more exact but because of computational limitations it can only constrain emissions over coarse regions. We find that the correction factors to the a priori CO emission inventory from the adjoint inversion are generally consistent with those of the analytical inversion when averaged over the large regions of the latter. The adjoint solution reveals fine-scale variability (cities, political boundaries) that the analytical inversion cannot resolve, for example, in the Indian subcontinent or between Korea and Japan, and some of that variability is of opposite sign which points to large aggregation errors in the analytical solution. Upward correction factors to Chinese emissions from the prior inventory are largest in central and eastern China, consistent with a recent bottom-up revision of that inventory, although the revised inventory also sees the need for upward corrections in southern China where the adjoint and analytical inversions call for downward correction. Correction factors for biomass burning emissions derived from the adjoint and analytical inversions are consistent with a recent bottom-up inventory on the basis of MODIS satellite fire data.” Kopacz, M., D. J. Jacob, D. K. Henze, C. L. Heald, D. G. Streets, and Q. Zhang (2009), J. Geophys. Res., 114, D04305, doi:10.1029/2007JD009264. [full text]
Model analysis of the factors regulating the trends and variability of carbon monoxide between 1988 and 1997 – Duncan & Logan (2008) “We used a 3-D model of chemistry and transport to investigate trends and variability in tropospheric carbon monoxide (CO) for 1988–1997 caused by changes in the overhead ozone column, fossil fuel emissions, biomass burning emissions, methane, and transport. We found that the decreasing CO burden in the northern extra-tropics (−0.85%/y) was more heavily influenced by the decrease in European emissions during our study period than by the similar increase in Asian emissions, as transport pathways from Europe favored accumulation at higher latitudes in winter and spring. However, the opposite trends in the CO burdens from these two source regions counterbalanced at lower latitudes. Elsewhere, the factors influencing CO often compete, diminishing their cumulative impact, and trends in model CO were small or insignificant for our study period, except in the tropics in boreal fall (1.1%/y), a result of emissions from major fires in Indonesia late in 1997. There was a decrease in the ozone column during the study period as a result of the phase of the solar cycle and the eruption of Pinatubo in 1991. This decrease contributed negatively to the trend in model CO by increasing the hydroxyl radical (OH). The impact of this negative contribution was diminished by a positive contribution of similar magnitude from increasing methane. However, the trends in these two factors did not cancel for tropospheric OH, which responded primarily to changes in the ozone column.” Duncan, B. N. and Logan, J. A., Atmos. Chem. Phys., 8, 7389-7403, doi:10.5194/acp-8-7389-2008, 2008. [full text]
Using CO2:CO correlations to improve inverse analyses of carbon fluxes – Palmer et al. (2006) “Observed correlations between atmospheric concentrations of CO2 and CO represent potentially powerful information for improving CO2 surface flux estimates through coupled CO2-CO inverse analyses. We explore the value of these correlations in improving estimates of regional CO2 fluxes in east Asia by using aircraft observations of CO2 and CO from the TRACE-P campaign over the NW Pacific in March 2001. Our inverse model uses regional CO2 and CO surface fluxes as the state vector, separating biospheric and combustion contributions to CO2. CO2-CO error correlation coefficients are included in the inversion as off-diagonal entries in the a priori and observation error covariance matrices. We derive error correlations in a priori combustion source estimates of CO2 and CO by propagating error estimates of fuel consumption rates and emission factors. However, we find that these correlations are weak because CO source uncertainties are mostly determined by emission factors. Observed correlations between atmospheric CO2 and CO concentrations imply corresponding error correlations in the chemical transport model used as the forward model for the inversion. These error correlations in excess of 0.7, as derived from the TRACE-P data, enable a coupled CO2-CO inversion to achieve significant improvement over a CO2-only inversion for quantifying regional fluxes of CO2.” Palmer, P. I., P. Suntharalingam, D. B. A. Jones, D. J. Jacob, D. G. Streets, Q. Fu, S. A. Vay, and G. W. Sachse (2006), J. Geophys. Res., 111, D12318, doi:10.1029/2005JD006697. [full text]
Adjoint inverse modeling of CO emissions over Eastern Asia using four-dimensional variational data assimilation – Yumimoto & Uno (2006) “We developed a four-dimensional variational (4DVAR) data assimilation system for a regional chemical transport model (CTM). In this study, we applied it to inverse modeling of CO emissions in the eastern Asia during April 2001 and demonstrated the feasibility of our assimilation system. Three ground-based observations were used for data assimilation. Assimilated results showed better agreement with observations; they reduced the RMS difference by 16–27%. Observations obtained on board the R/V Ronald H. Brown were used for independent validation of the assimilated results. The CO emissions over industrialized east central China between Shanghai and Beijing were increased markedly by the assimilation. The results show that the annual anthropogenic (fossil and biofuel combustion) CO emissions over China are 147 Tg. Sensitivity analyses using the adjoint model indicate that the high CO concentration measured on 17 April at Rishiri, Japan (which the assimilation was unable to reproduce) originated in Russia or had traveled from outside the Asian region (e.g. Europe).” Keiya Yumimoto and Itsushi Uno, Atmospheric Environment, Volume 40, Issue 35, November 2006, Pages 6836-6845, doi:10.1016/j.atmosenv.2006.05.042.
Improved quantification of Chinese carbon fluxes using CO2/CO correlations in Asian outflow – Suntharalingam et al. (2004) “We use observed CO2:CO correlations in Asian outflow from the TRACE-P aircraft campaign (February–April 2001), together with a three-dimensional global chemical transport model (GEOS-CHEM), to constrain specific components of the east Asian CO2 budget including, in particular, Chinese emissions. The CO2/CO emission ratio varies with the source of CO2 (different combustion types versus the terrestrial biosphere) and provides a characteristic signature of source regions and source type. Observed CO2/CO correlation slopes in east Asian boundary layer outflow display distinct regional signatures ranging from 10–20 mol/mol (outflow from northeast China) to 80 mol/mol (over Japan). Model simulations using best a priori estimates of regional CO2 and CO sources from Streets et al.  (anthropogenic), the CASA model (biospheric), and Duncan et al.  (biomass burning) overestimate CO2 concentrations and CO2/CO slopes in the boundary layer outflow. Constraints from the CO2/CO slopes indicate that this must arise from an overestimate of the modeled regional net biospheric CO2 flux. Our corrected best estimate of the net biospheric source of CO2 from China for March–April 2001 is 3200 Gg C/d, which represents a 45% reduction of the net flux from the CASA model. Previous analyses of the TRACE-P data had found that anthropogenic Chinese CO emissions must be ∼50% higher than in Streets et al.’s  inventory. We find that such an adjustment improves the simulation of the CO2/CO slopes and that it likely represents both an underreporting of sector activity (domestic and industrial combustion) and an underestimate of CO emission factors. Increases in sector activity would imply increases in Chinese anthropogenic CO2 emissions and would also imply a further reduction of the Chinese biospheric CO2 source to reconcile simulated and observed CO2 concentrations.” Suntharalingam, P., D. J. Jacob, P. I. Palmer, J. A. Logan, R. M. Yantosca, Y. Xiao, M. J. Evans, D. G. Streets, S. L. Vay, and G. W. Sachse (2004), J. Geophys. Res., 109, D18S18, doi:10.1029/2003JD004362. [full text]
Evaluation of pollutant outflow and CO sources during TRACE-P using model-calculated, aircraft-based, and Measurements of Pollution in the Troposphere (MOPITT)-derived CO concentrations – Allen et al. (2004) “Outflow of CO from Asia during March 2001 is evaluated using data from the Transport and Chemical Evolution over the Pacific (TRACE-P) mission and the Measurements of Pollution in the Troposphere (MOPITT) instrument in conjunction with model-calculated CO from the University of Maryland chemistry and transport model (UMD CTM). Comparison of model-calculated CO with aircraft measurements indicates that temporal and spatial variations in CO are well captured by the model (mean correlation coefficient of 0.78); however, model-calculated mixing ratios are lower than observed especially for pressures >850 hPa where negative biases of ∼60 ppbv were seen. Regression analysis is used to optimize the magnitudes of the bottom-up TRACE-P Asian fossil fuel (FF), biofuel (BF), and biomass burning (BB) CO emission inventories. Resulting Asian scaling factors are 1.59 ± 0.34 for FF + BF emissions and 0.47 ± 0.46 for BB emissions. Resulting FF + BF emissions are 27.7 ± 6.1 Tg for March 2001 (301 ± 67 Tg for an entire year). Resulting BB emissions for March 2001 are 8.5 ± 8.3 Tg. These results are consistent with recent inverse modeling studies. Scaling factors are lowest (highest) for experiments that assume a high (low) CO yield for the oxidation of anthropogenic and natural hydrocarbons and for experiments that use (do not use) an aerosol-modified OH distribution. Comparison of model-calculated CO with MOPITT measurements supports the results from our regression analysis. Without exception, mean March 2001 model-calculated CO profiles in the TRACE-P region from a simulation with adjusted CO sources are within a standard deviation of mean March 2001 MOPITT-sampled profiles.” Allen, D., K. Pickering, and M. Fox-Rabinovitz (2004), J. Geophys. Res., 109, D15S03, doi:10.1029/2003JD004250.
Monthly CO surface sources inventory based on the 2000–2001 MOPITT satellite data – Pétron et al. (2004) “This paper presents results of the inverse modeling of carbon monoxide surface sources on a monthly and regional basis using the MOPITT (Measurement Of the Pollution In The Troposphere) CO retrievals. The targeted time period is from April 2000 to March 2001. A sequential and time-dependent inversion scheme is implemented to correct an a priori set of monthly mean CO sources. The a posteriori estimates for the total anthropogenic (fossil fuel + biofuel + biomass burning) surface sources of CO in TgCO/yr are 509 in Asia, 267 in Africa, 140 in North America, 90 in Europe and 84 in Central and South America. Inverting on a monthly scale allows one to assess a corrected seasonality specific to each source type and each region. Forward CTM simulations with the a posteriori emissions show a substantial improvement of the agreement between modeled CO and independent in situ observations.” Pétron, G., C. Granier, B. Khattatov, V. Yudin, J.-F. Lamarque, L. Emmons, J. Gille, and D. P. Edwards (2004), Geophys. Res. Lett., 31, L21107, doi:10.1029/2004GL020560. [full text]
Comparative inverse analysis of satellite (MOPITT) and aircraft (TRACE-P) observations to estimate Asian sources of carbon monoxide – Heald et al. (2004) “We use an inverse model analysis to compare the top-down constraints on Asian sources of carbon monoxide (CO) in spring 2001 from (1) daily MOPITT satellite observations of CO columns over Asia and the neighboring oceans and (2) aircraft observations of CO concentrations in Asian outflow from the TRACE-P aircraft mission over the northwest Pacific. The inversion uses the maximum a posteriori method (MAP) and the GEOS-CHEM chemical transport model (CTM) as the forward model. Detailed error characterization is presented, including spatial correlation of the model transport error. Nighttime MOPITT observations appear to be biased and are excluded from the inverse analysis. We find that MOPITT and TRACE-P observations are independently consistent in the constraints that they provide on Asian CO sources, with the exception of southeast Asia for which the MOPITT observations support a more modest decrease in emissions than suggested by the aircraft observations. Our analysis indicates that the observations do not allow us to differentiate source types (i.e., anthropogenic versus biomass burning) within a region. MOPITT provides ten pieces of information to constrain the geographical distribution of CO sources, while TRACE-P provides only four. The greater information from MOPITT reflects its ability to observe all outflow and source regions. We conducted a number of sensitivity studies for the inverse model analysis using the MOPITT data. Temporal averaging of the MOPITT data (weekly and beyond) degrades the ability to constrain regional sources. Merging source regions beyond what is appropriate after careful selection of the state vector leads to significant aggregation errors. Calculations for an ensemble of realistic assumptions lead to a range of inverse model solutions that has greater uncertainty than the a posteriori errors for the MAP solution. Our best estimate of total Asian CO sources is 361 Tg yr−1, over half of which is attributed to east Asia.” Heald, C. L., D. J. Jacob, D. B. A. Jones, P. I. Palmer, J. A. Logan, D. G. Streets, G. W. Sachse, J. C. Gille, R. N. Hoffman, and T. Nehrkorn (2004), J. Geophys. Res., 109, D23306, doi:10.1029/2004JD005185. [full text]
Inverting for emissions of carbon monoxide from Asia using aircraft observations over the western Pacific – Palmer et al. (2003) “We use aircraft observations of continental outflow over the western Pacific from the Transport and Chemical Evolution over the Pacific (TRACE-P) mission (March–April 2001), in combination with an optimal estimation inverse model, to improve emission estimates of carbon monoxide (CO) from Asia. A priori emissions and their errors are from a customized bottom-up Asian emission inventory for the TRACE-P period. The global three-dimensional GEOS-CHEM chemical transport model (CTM) is used as the forward model. The CTM transport error (20–30% of the CO concentration) is quantified from statistics of the difference between the aircraft observations of CO and the forward model results with a priori emissions, after removing the mean bias which is attributed to errors in the a priori emissions. Additional contributions to the error budget in the inverse analysis include the representation error (typically 5% of the CO concentration) and the measurement accuracy (≃2% of the CO concentration). We find that the inverse model can usefully constrain five sources: Chinese fuel consumption, Chinese biomass burning, total emissions from Korea and Japan, total emissions from Southeast Asia, and the ensemble of all other sources. The inversion indicates a 54% increase in anthropogenic emissions from China (to 168 Tg CO yr−1) relative to the a priori; this value is still much lower than had been derived in previous inversions using the CMDL network of surface observations. A posteriori emissions of biomass burning in Southeast Asia and China are much lower than a priori estimates.” Palmer, P. I., D. J. Jacob, D. B. A. Jones, C. L. Heald, R. M. Yantosca, J. A. Logan, G. W. Sachse, and D. G. Streets (2003), J. Geophys. Res., 108(D21), 8828, doi:10.1029/2003JD003397. [full text]
Reanalysis of tropospheric CO trends: Effects of the 1997–1998 wildfires – Novelli et al. (2003) “For the past decade NOAA/CMDL has measured tropospheric carbon monoxide from a global network of sampling sites. The resulting data set provides an internally consistent picture of CO in the lower troposphere that is used to study its distribution, trends and budget. All measurements were referenced to the so-called CMDL Reference Scale (WMO 88), which was based on two sets of primary standards produced at CMDL during the late 1980s and early 1990s. A long-term downward trend in tropospheric CO during the 1990s, overlaid with shorter periods of increase and decrease, was indicated from the air measurements. Primary standards prepared in 1999 and 2000 suggested that the scale had drifted upward over time, and that mixing ratios determined in field samples were underestimated. We have applied a time dependent correction to our CO measurements based upon four sets of primary standards. In this paper, we describe the revision of the CO scale and our atmospheric measurements. A reanalysis of tropospheric trends through 2001 was based on the revised global data set. The results support previous reports of a decline in tropospheric CO. This decrease is now found largely confined to the Northern Hemisphere, where dramatic reductions in fossil fuel emissions have reportedly occurred. In contrast, no significant trend is determined in the Southern Hemisphere between 1991 and 2001. Globally averaged CO exhibits large interannual variability, primarily reflecting year to year changes in emissions from biomass burning. Dramatic enhancements of tropospheric CO in 1997 and 1998 resulted from exceptionally widespread wildfires which provided a strong pulse of CO to the atmosphere. In years of extensive boreal biomass burning, fire emissions can perturb CO levels over regional and global scales, disturbing oxidation/reduction chemistry in the troposphere.” Novelli, P. C., K. A. Masarie, P. M. Lang, B. D. Hall, R. C. Myers, and J. W. Elkins (2003), J. Geophys. Res., 108(D15), 4464, doi:10.1029/2002JD003031. [full text]
Global distribution of carbon monoxide – Holloway et al. (2000) “This study explores the evolution and distribution of carbon monoxide (CO) using the National Oceanic and Atmospheric Administration (NOAA) Geophysical Fluid Dynamics Laboratory three-dimensional global chemical transport model (GFDL GCTM). The work aims to gain an improved understanding of the global carbon monoxide budget, specifically focusing on the contribution of each of the four source terms to the seasonal variability of CO. The sum of all CO sources in the model is 2.5 Pg CO/yr (1 Pg = 103 Tg), including fossil fuel use (300 Tg CO/yr), biomass burning (748 Tg CO/yr), oxidation of biogenic hydrocarbons (683 Tg CO/yr), and methane oxidation (760 Tg CO/yr). The main sink for CO is destruction by the hydroxyl radical, and we assume a hydroxyl distribution based on three-dimensional monthly varying fields given by Spivakovsky et al. , but we increase this field by 15% uniformly to agree with a methyl chloroform lifetime of 4.8 years [Prinn et al, 1995]. Our simulation produces a carbon monoxide field that agrees well with available measurements from the NOAA/Climate Monitoring and Diagnostics Laboratory global cooperative flask sampling network and from the Jungfraujoch observing station of the Swiss Federal Laboratories for Materials Testing and Research (EMPA) (93% of seasonal-average data points agree within ±25%) and flight data from measurement campaigns of the NASA Global Tropospheric Experiment (79% of regional-average data points agree within ±25%). For all 34 ground-based measurement sites we have calculated the percentage contribution of each CO source term to the total model-simulated distribution and examined how these contributions vary seasonally due to transport, changes in OH concentration, and seasonality of emission sources. CO from all four sources contributes to the total magnitude of CO in all regions. Seasonality, however, is usually governed by the transport and destruction by OH of CO emitted by fossil fuel and/or biomass burning. The sensitivity to the hydroxyl field varies spatially, with a 30% increase in OH yielding decreases in CO ranging from 4–23%, with lower sensitivities near emission regions where advection acts as a strong local sink. The lifetime of CO varies from 10 days over summer continental regions to well over a year at the winter poles, where we define lifetime as the turnover time in the troposphere due to reaction with OH.” Holloway, T., H. Levy II, and P. Kasibhatla (2000), J. Geophys. Res., 105(D10), 12,123–12,147, doi:10.1029/1999JD901173.
Carbon monoxide in the U.S. mid‐Atlantic troposphere: Evidence for a decreasing trend – Hallock-Waters et al. (1999) “Nearly continuous measurements of carbon monoxide (CO) were made at Shenandoah National Park‐Big Meadows in rural Virginia, a site considered representative of regional air quality, from December 1994 to November 1997. Similar observations were also made at this location from October 1988 to October 1989. These observations combine to indicate a decreasing trend in CO concentration over the U.S. mid‐Atlantic region of about 5.0 ppbv yr−1, with greater than 95% confidence that the slope is significantly different from zero. The decrease suggests U.S. reductions in anthropogenic CO emissions have been effective in reducing pollutant levels. The observed trend is consistent with the U.S. EPA reported trend in emissions and the decrease in Northern Hemisphere tropospheric background CO mixing ratios observed by other researchers.” Hallock‐Waters, K. A., B. G. Doddridge, R. R. Dickerson, S. Spitzer, and J. D. Ray (1999), Geophys. Res. Lett., 26(18), 2861–2864, doi:10.1029/1999GL900609. [full text]
Distributions and recent changes of carbon monoxide in the lower troposphere – Novelli et al. (1998) “Since 1988, the distribution of carbon monoxide (CO) in the lower troposphere has been determined using a globally distributed air sampling network. Site locations range from 82°N to 90°S, with wide longitudinal coverage, and represent the marine boundary layer, regionally polluted atmospheres, and the free troposphere. These measurements present a unique, intercalibrated, and internally consistent data set that are used to better define the global temporal and spatial distribution of CO. In this paper, times series from 49 sites are discussed. With an average lifetime of ∼2 months, CO showed significant concentration gradients. In the marine boundary layer, mixing ratios were greatest in the northern winter (200–220 ppb) and lowest in the southern summer (35–45 ppb). The interhemispheric gradient showed strong seasonality with a maximum difference between the high latitudes of the northern and southern hemispheres (160–180 ppb) in February and March and a minimum in July and August (10–20 ppb). Higher CO was found in regions near human development relative to those over more remote areas. The distributions provide additional evidence of the widespread pollution of the lower atmosphere. Remote areas in the high northern hemisphere are polluted by anthropogenic activities in the middle latitudes, and those in the southern hemisphere are heavily influenced by the burning of biomass in the tropics. While tropospheric concentrations of CO exhibit periods of increase and decrease, the globally averaged CO mixing ratio over the period from 1990 through 1995 decreased at a rate of approximately 2 ppb yr−1.” Novelli, P. C., K. A. Masarie, and P. M. Lang (1998), J. Geophys. Res., 103(D15), 19,015–19,033, doi:10.1029/98JD01366. [full text]
An internally consistent set of globally distributed atmospheric carbon monoxide mixing ratios developed using results from an intercomparison of measurements – Novelli et al. (1998) “The Measurement of Air Pollution from Satellite (MAPS) instrument measures carbon monoxide (CO) in the middle troposphere from a space platform. In anticipation of the deployment of MAPS aboard the space shuttle Endeavor for two 10-day missions in 1994, plans were made to prepare a set of correlative measurements which would be used as part of the mission validation program. Eleven laboratories participated in the correlative measurement program by providing NASA with the results of their CO field programs during April and October 1994. Measurements of CO in the boundary layer, while not used in the MAPS validation, provide a picture of CO in the lower troposphere. Because measurements of CO made by different laboratories have been known to differ significantly, all correlative team members participated in an intercomparison of their measurements to define potential differences in techniques and calibration scales. While good agreement was found between some laboratories, there were differences between others. The use of similar analytical techniques and calibration scales did not always provide similar results. The results of the intercomparisons were used to normalize all ground-based measurements to the National Oceanic and Atmospheric Administration/Climate Monitoring and Diagnostics Laboratory CO reference scale. These data provide an internally consistent picture of CO in thelower atmosphere during spring and fall 1994.” Novelli, P. C., et al. (1998), J. Geophys. Res., 103(D15), 19,285–19,293, doi:10.1029/97JD00031.
Recent Changes in Atmospheric Carbon Monoxide – Novelli et al. (1994) “Measurements of carbon monoxide (CO) in air samples collected from 27 locations between 71°N and 41°S show that atmospheric levels of this gas have decreased worldwide over the past 2 to 5 years. During this period, CO decreased at nearly a constant rate in the high northern latitudes. In contrast, in the tropics an abrupt decrease occurred beginning at the end of 1991. In the Northern Hemisphere, CO decreased at a spatially and temporally averaged rate of 7.3 (±0.9) parts per billion per year (6.1 percent per year) from June 1990 to June 1993, whereas in the Southern Hemisphere, CO decreased 4.2 (±0.5) parts per billion per year (7.0 percent per year). This recent change is opposite a long-term trend of a 1 to 2 percent per year increase inferred from measurements made in the Northern Hemisphere during the past 30 years.” Paul C. Novelli, Ken A. Masarie, Pieter P. Tans and Patricia M. Lang, Science 18 March 1994: Vol. 263 no. 5153 pp. 1587-1590, DOI: 10.1126/science.263.5153.1587.
Mixing Ratios of Carbon Monoxide in the Troposphere – Novelli et al. (1992) “Carbon monoxide (CO) mixing ratios were measured in air samples collected weekly at eight locations. The air was collected as part of the CMDL/NOAA cooperative flask sampling program (Climate Monitoring and Diagnostics Laboratory, formerly Geophysical Monitoring for Climatic Change, Air Resources Laboratory/National Oceanic and Atmospheric Administration) at Point Barrow, Alaska (71°N), Niwot Ridge, Colorado (40°N), Mauna Loa and Cape Kumakahi, Hawaii (19°N), Guam, Marianas Islands (13°N), Christmas Island (2°N), Ascension Island (8°S) and American Samoa (14°S). Half-liter or 3-L glass flasks fitted with glass piston stopcocks holding teflon O rings were used for sample collection. CO levels were determined within several weeks of collection using gas chromatography followed by mercuric oxide reduction detection, and mixing ratios were referenced against the CMDL/NOAA carbon monoxide standard scale. During the period of study (mid-1988 through December 1990) CO levels were greatest in the high latitudes of the northern hemisphere (mean mixing ratio from January 1989 to December 1990 at Point Barrow was approximately 154 ppb) and decreased towards the south (mean mixing ratio at Samoa over a similar period was 65 ppb). Mixing ratios varied seasonally, the amplitude of the seasonal cycle was greatest in the north and decreased to the south. Carbon monoxide levels were affected by both local and regional scale processes. The difference in CO levels between northern and southern latitudes also varied seasonally. The greatest difference in CO mixing ratios between Barrow and Samoa was observed during the northern winter (about 150 ppb). The smallest difference, 40 ppb, occurred during the austral winter. The annually averaged CO difference between 71°N and 14°S was approximately 90 ppb in both 1989 and 1990; the annually averaged interhemispheric gradient from 71°N to 41°S is estimated as approximately 95 ppb.” Novelli, P. C., L. P. Steele, and P. P. Tans (1992), J. Geophys. Res., 97(D18), 20,731–20,750, doi:10.1029/92JD02010.
The global cycle of carbon monoxide: Trends and mass balance – Khalil & Rasmussen (1990) “The annual global emissions of CO are estimated to be about 2,600 ± 600 Tg, of which about 60% are from human activities including combustion of fossil fuels and oxidation of hydrocarbons including methane. The remaining 40% of the emissions are from natural processes, mostly from the oxidation of hydrocarbons but also from plants and the oceans. Almost all the CO emitted into the atmosphere each year is removed by reactions with OH radicals (85%), by soils (10%), and by diffusion into the stratosphere. There is a small imbalance between annual emissions and removal, causing an increase of about 1% per year. It is very likely that the imbalance is due to increasing emissions from anthropogenic activities. The average concentration of CO is about 90 ppbv, which amounts to about 400 Tg in the atmosphere, and the average lifetime is about 2 months. This view of the global cycle of CO is consistent with the present estimates of average OH concentrations and the budgets of other trace gases including methane and methylchloroform. There are large remaining uncertainties that may in the future upset the apparently cohesive present budget of CO. If the present view of the global cycle of CO is correct, then it is likely that, in time, increasing levels of CO will contribute to widespread changes in atmospheric chemistry.” M.A.K. Khalil, a and R.A. Rasmussen, Chemosphere, Volume 20, Issues 1-2, 1990, Pages 227-242, doi:10.1016/0045-6535(90)90098-E.
Spectroscopic measurements of atmospheric carbon monoxide and methane. 1: latitudinal distribution – Dianov-Klokov et al. (1989) “The results of spectroscopic total column measurements of CO and CH4 at different points of the Northern and Southern Hemispheres in 1970–1985, are reported. Seasonal cycles of CO are evident for all the sites. The Northern Hemispheric long-term positive trend of CO seems to be 1.5–2% per year. In the Southern Hemisphere, temporal increasing was not detected and a possible upper limit for it is about 0.6% per year. Methane concentration in the Northern Hemisphere increases at a rate of 1.2% per year.” V. I. Dianov-Klokov, L. N. Yurganov, E. I. Grechko and A. V. Dzhola, Journal of Atmospheric Chemistry, Volume 8, Number 2, 139-151, DOI: 10.1007/BF00053719. [full text]
Spectroscopic measurements of atmospheric carbon monoxide and methane. 2: Seasonal variations and long-term trends – Dianov-Klokov & Yurganov (1989) “A spectroscopic technique for measuring CO and CH4 contents is described and the latitudinal distributions of these gases are presented. Carbon monoxide abundance decreases southward, having two local maxima: in midlatitudes and in the tropics. The slope of latitude dependence varies according to the season of the year. The difference in CH4 content does not exceed the accuracy of the method (±8%).” V. I. Dianov-Klokov and L. N. Yurganov, Journal of Atmospheric Chemistry, Volume 8, Number 2, 153-164, DOI: 10.1007/BF00053720.
A survey of continental concentrations of atmospheric CO in the southern hemisphere – Kirchhoff & Marinho (1989) “The first large scale survey of surface CO concentrations at Southern Hemisphere continental sites is described. Marine sites are compared to sites with a true continental character with the objective to identify different ecological surface conditions in terms of CO concentrations. The marine sites at the Atlantic coast show the lowest concentrations, about 100 ppbv, whereas the sites in the savannah region show concentrations 3 times as large owing to the influence of nearby biomass burning activity. The observations were highly variable, with one result as high as 700 ppbv. These high values are comparable to sites near urban developments. Sites in the Amazonian rain forest show concentrations as low as the coastal sites, on the average, but sporadic peaks have been seen when air masses are brought in from city areas or from large forest fires.” V.W.J.H. Kirchhoff and E.V.A. Marinho, Atmospheric Environment, Volume 23, Issue 2, 1989, Pages 461-466, doi:10.1016/0004-6981(89)90589-1.
Carbon monoxide in the Earth’s atmosphere: indications of a global increase – Khalil & Rasmussen (1988) “Over half of the carbon monoxide in the atmosphere comes from human activities including motor traffic, other combustion of fossil fuels, and slash and burn agriculture1–4. Additional anthropogenic sources include the burning of wood, savannah lands, and the oxidation of hydrocarbons including methane. Over the years these sources have increased gradually and may have already caused the concentrations of CO to double since pre-industrial times when human activities did not significantly affect the global cycles of CO and other trace gases. Increasing levels of CO can lead to an increase of tropospheric O3 (refs 5,6) and a build-up of many other trace gases in the Earth’s atmosphere, which may in turn cause widespread perturbations of tropospheric chemistry, global warming, and other climatic changes7. In a recent report8 to senior US Government officials the National Academies stated the urgent need to know the global distribution and trends of CO. During the past 6–8 years we have taken systematic measurements of CO at sites ranging from within the Arctic Circle to the South Pole. The rates of increase of the globally averaged concentration are between 0.8% and 1.4% per year depending on the statistical method used for estimating the trends. These increases may have gone on for much longer because more than half of the atmospheric CO now comes from anthropogenic sources. We find that the rates of increase are largest at mid-northern and tropical latitudes, where most of the sources are located.” M. A. K. Khalil & R. A. Rasmussen, Nature 332, 242 – 245 (17 March 1988); doi:10.1038/332242a0.
The seasonality of CO abundance in the Southern Hemisphere – Seiler et al. (1984) “CO mixing ratios in air have been measured continuously at Cape Point (34°21prime;S; 18°29’E) between 1978 and 1981. The results show a seasonal variation of the CO mixing ratios with minimum values of 53 p.p.b.v. during January/February and maximum values of 87 p.p.b.v. during September/October. Short-term variations of CO mixing ratios in clean, undisturbed air were lacking, indicating that CO is well mixed in the Southern Hemisphere at latitudes of 20–40° S and that the observed seasonal variation is not due to temporal changes of local and regional source strengths. The seasonality of CO is explained by the seasonal variation of OH and by the north–south shift of the intertropical convergence zone. The agreement of CO mixing ratios measured at Cape Point and over the Southern Atlantic in 1971/1972 indicates that the southern hemispheric CO mixing ratios cannot have changed by more than 5–10% during the last decade.” Wolfgang Seiler, Helmut Giehl, Ernst-Günther Brunke, Eric Halliday, Tellus B, Volume 36B, Issue 4, pages 219–231, September 1984, DOI: 10.1111/j.1600-0889.1984.tb00244.x.
The Distribution of Carbon Monoxide and Ozone in the Free Troposphere – Seiler & Fishman (1981) “The two-dimensional distributions of CO and O3 in the free troposphere during July and August, 1974, are discussed. The data confirm the previous findings that both of these gases are considerably more abundant in the northern hemisphere, but the degree of the asymmetry is somewhat different from what had been reported previously, especially for CO. When examined with respect to other available data sets, the conclusion is drawn that a pronounced seasonal cycle exists for CO in both hemispheres which may be driven by the likely seasonal cycle of the OH radical. The data also indicate that CO concentrations exhibit significant variability with height in the northern hemisphere, whereas southern hemispheric concentrations are quite constant with altitude except in cases where interhemispheric exchange of air may be occurring. A discussion on the vertical and horizontal transport processes inferred from the CO and O3 measurements is presented. The possible interdependence of the photochemical cycles of these two trace gases is also discussed.” Seiler, W., and J. Fishman (1981), J. Geophys. Res., 86(C8), 7255–7265, doi:10.1029/JC086iC08p07255.
The cycle of atmospheric CO – Seiler (1974) “New measurements of the CO-mixing ratio in the two hemispheres with the dissolved CO in surface seawater together with previous results are used to set up a detailed budget of CO in the atmosphere. It is shown that CO is produced by technological and by natural sources. The source strengths of both kinds of sources are of the same magnitude. The total CO-production rate is estimated to be 10 × 1014 g per year. The corresponding residence time is 0.5 years. From the observed latitudinal CO-distribution between the hemispheres the production of CO by the oxidation of methane in the troposphere is judged to be a minor source. CO is removed by microbiological processes at the soil surfaces, by photochemical consumption in the stratosphere, and probably also by reaction with OH radicals in the troposphere.” Wolfgang Seiler, Tellus, Volume 26, Issue 1-2, pages 116–135, February 1974, DOI: 10.1111/j.2153-3490.1974.tb01958.x.
The Abundance of Atmospheric Carbon Monoxide above Columbus, Ohio – Shaw (1958) “From measurements of the line R(3) of the 4.7 μ fundamental band appearing in the solar spectrum, the usual CO content of the atmosphere above Columbus, Ohio, during1952-53 has been found to be between 0.04 and 0.07 atm-cm/air mass. There is evidence for some increase in CO content on occasional days during the colder months of the year, but, because the line measured is contaminated by a weak H2O absorption, it is not possible to show that similar increases also occur during the summer months. The occasions of high CO contentare usually associated with periods of low visibility and usually occur during the early part of the day. This is especially true of the period October 20-November 13, 1952, when the worst forest fires for twenty years were burning in southeastern Ohio and states farther south. The present data are compared with the results of other workers.” Shaw, J. H., Astrophysical Journal, vol. 128, p.428, 1958. [full text]
The absorption due to carbon monoxide in the infrared solar spectrum – Locke & Herzberg (1953) “New tracings of the absorption bands due to carbon monoxide in the 4.7 μ and 2.4 μ regions of the solar spectrum were obtained with a spectrometer of high resolving power. From the observed absorption intensity at 4.7 μ the abundance of carbon monoxide in the earth’s atmosphere over Ottawa was found, during spring and fall 1952, to vary between 0.1 and 0.2 cm-atm. Similar observations, made at other stations, were re-evaluated with the laboratory data used at Ottawa. The values for the carbon monoxide abundance in the earth’s atmosphere at different geographical locations, determined in this way, were found to be within the limits of the values obtained at Ottawa. Absorption lines due to solar carbon monoxide in the 4.7 μ region of the spectrum were resolved. Their intensity relative to the intensity of the solar carbon monoxide absorption in the 2.4 μ region of the spectrum was found to be in agreement with expectations based on the theoretical curves of growth for solar absorption lines.” J. L. Locke and L. Herzberg, Can. J. Phys. 31(4): 504–516 (1953), doi:10.1139/p53-050.
Investigations of Atmospheric CO at the Jungfraujoch – Benesch et al. (1953) “Analysis of high-resolution solar spectra taken at the Jungfraujoch in Switzerland indicates that the terrestrial atmospheric CO content may vary by a factor of five in extreme cases, and is, furthermore, subject to surprisingly large fluctuations within the period of one hour. These variations are apparently unrelated to the more readily available data on general meteorological conditions, but a mechanism is suggested wherein the fluctuations of the CO may depend on atmospheric irregularities of a more finely detailed nature than those which normally come into consideration in meteorological observations.” W. Benesch, M. Migeotte, and L. Neven, JOSA, Vol. 43, Issue 11, pp. 1119-1123 (1953), doi:10.1364/JOSA.43.001119.
Identification of Carbon Monoxide in the Atmosphere above Flagstaff, Arizona – Adel (1952) No abstract. Adel, Arthur, Astrophysical Journal, vol. 116, p.442, 1952. [full text]
The Fundamental Band of Carbon Monoxide at 4.7μ in the Solar Spectrum – Migeotte (1949) No abstract available, but according to Shaw (1958) this is first identification of CO in Earth’s atmosphere. Marcel V. Migeotte, Phys. Rev. 75, 1108–1109 (1949).